Loss tolerant transmission control protocol

ABSTRACT

Provided are apparatuses and methods for transmitting or receiving data packets in a data block in a communication network with a transport protocol. In one example, a loss tolerant TCP protocol is used in which a maximum segment size (MSS) may be adapted to a minimum granularity of a congestion window. Also, proactive forward error correction (FEC) packets may be added to a window of the data block. The number of proactive FEC packets may be determined, for example, based on an estimate erasure rate. In addition, reactive FEC packets may be added to the data block. Also, a receiver may receive data packets in a data block and process a selective acknowledgment (SACK) responsive to the data packets received.

This application claims the benefit of U.S. Provisional Application Ser.No. 60/666,398, filed Mar. 30, 2005, which is incorporated herein in itsentirety.

FIELD OF THE INVENTION

The invention relates generally to communication networks. Morespecifically, the invention provides for improved communicationperformance over lossy links.

BACKGROUND OF THE INVENTION

Data communication over wireless channels has become increasinglycommon. For example, WiFi is used for wireless communication forconnections based on the IEEE 802.11 standard. Many other wirelesschannels may be used such as WiMAX, 3G, mesh networks, or communitynetworks, to name a few. Wireless channels may be lossy such that datamay often be lost during transmission due to any one of a variety ofconditions. For example, weather conditions may be such that thetransmission of communication data may be impaired. Likewise, there maybe interference to data transmission from a variety of causes such asinterference from other devices transmitting on the same channel. Any ofthese factors may contribute to additional loss in data packettransmission or increased data packet erasure rates.

In end-to-end transport protocols (e.g., Transmission Control Protocol(TCP)) data communication is provided across interconnected networks ordevices. In such transport protocols, of which TCP is one example, datato be transmitted is broken into packets of data. The data packets aretransmitted to a receiver where the packets are verified and reassembledinto the original message. An acknowledgement (ACK) is returned from thereceiver to indicate that the data packets were received. If an ACK isnot returned, the data packet may have to be re-transmitted. Inaddition, when the sender does not receive the ACK within a specifiedperiod of time, the transport protocol at the sender may timeout. Thisresults in a reduced rate of transmission of packets as the transportprotocol interprets the lack of an ACK as congestion in the network.Then, the data packets may be re-transmitted by the transport protocolat the sender.

TCP, being one example of an end-to-end transport protocol, has becomethe dominant transmission protocol in use. However, TCP also suffersperformance degradation, particularly in wireless links due to suchproblems as high bit error rates, packet erasure, or intermittentconnectivity. In addition, data packet erasures and loss may negativelyimpact performance through TCP timeouts. Such problems are found inother transport layer protocols as well (e.g., UDP, integrated withmedia streaming or VoIP, or any wireless link-layer design). Congestionmay occur in a network when an amount of traffic on a communication linkor path exceeds the capacity of the link or path. In such cases, excessdata may be discarded or excess data may be buffered until congestioneases. If congestion persists, however, the congestion is controlled bydiscarding data packets in the buffer to clear the buffer in apacket-switched network.

TCP is typically used for congestion control in the event of packetloss. However, when data packet loss is not due to congestion (e.g.,packet loss due to packet erasure or loss of packets in a lossy wirelesslink), TCP performance may suffer from unnecessary congestion control.Such congestion control may cause TCP to underestimate capacity whichresults in a reduction of the congestion window and underutilization ofavailable capacity. TCP suffers substantial performance degradation withlong latency channels that even have only a 1% residual error rate. Theconfusion between congestion and non-congestive loss exists for othertransport protocols as well.

Moreover, channel impairments or interference may also result in signalto noise ratio (SNR) degradation and bit errors which may in turn resultin packet errors or erasures.

Thus, there exists a need for a method and system for reducingperformance loss in a wireless communication network and enhancingtransport layer protocol performance in lossy communication channels dueto misinterpretation of the loss as being related to congestion. Thereis also a need for a method and system to adapt data segment size toincrease network resiliency to bit or packet erasures.

SUMMARY OF THE INVENTION

The following presents a simplified summary in order to provide a basicunderstanding of some aspects of the invention. The summary is not anextensive overview of the invention. It is neither intended to identifykey or critical elements of the invention nor to delineate the scope ofthe invention. The following summary merely presents some concepts ofthe invention in a simplified form as a prelude to the more detaileddescription below.

In one example of the present invention, a method is provided fortransmitting data packets in a data window with a transport protocol. Inone example, the window granularity may be determined or adjusted basedon a Maximum Segment Size (MSS).

In yet another example, a number of proactive Forward Error Correction(FEC) packets may be determined and added to the data window and theratio of the FEC packets to data packets in the data window may bedetermined.

In another example, the MSS may be adapted to accommodate the proactiveFEC packets at a determined window granularity.

In another example, a method is provided for creating a data block. Inone example of creating a data block, a number of data packets and FECpackets are included in a data window. In another example, the ratio ofFEC packets to data packets is adjusted. In one example, the ratio isadjusted based on an estimated loss rate.

In another example, a transport protocol may reduce the congestionwindow when an Explicit Congestion Notification (ECN) is received. Forexample, the response to ECN may provide a distinction betweencongestion and erasure loss. In another example, on receiving an ECN,the size of the window in bytes may be reduced for different data/FECparameters in subsequent blocks/windows.

In another example, a method is provided for adjusting windowgranularity based on a maximum packet size. In another example, minimumpacket size is used.

In another example, a method is provided for adjusting windowgranularity based on a current Maximum Segment Size (MSS).

In another example, a method is provided for transmission of reactivepackets.

In another example, a method is provided decoding a packet at areceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and theadvantages thereof may be acquired by referring to the followingdescription in consideration of the accompanying drawings, in which likereference numbers indicate like features, and wherein:

FIG. 1 illustrates an example of a network in which various aspects ofthe present invention may be implemented.

FIGS. 2A-2C are block diagrams illustrating an example of data packetstransmitted in a data block with adaptive channel capacity in which oneor more illustrative embodiments of the invention may be implemented.

FIG. 3 is a diagram illustrating components of LT-TCP (Loss TolerantTCP) in which one or more illustrative embodiments of the invention maybe implemented.

FIG. 4A illustrates an example of transmission of data packets andtimeout in which one or more illustrative embodiments of the inventionmay be implemented.

FIG. 4B illustrates an example of total transmission loss.

FIGS. 5A and 5B illustrate an example of the effects of windowgranularity on timeout and re-transmission of data packets in which oneor more illustrative embodiments of the invention may be implemented.

FIG. 6 illustrates an example of recovery of FEC data packets in whichone or more illustrative embodiments of the invention may beimplemented.

FIG. 7 illustrates an example of a block of data packets includingproactive and reactive FECs in which one or more illustrativeembodiments of the invention may be implemented.

FIG. 8 is an example of proactive FEC data packets in a transmission inwhich one or more illustrative embodiments of the invention may beimplemented.

FIG. 9 is an example of re-transmission of lost data packets in whichone or more illustrative embodiments of the invention may beimplemented.

FIG. 10 illustrates an example in which reactive FEC data packets may beused to re-transmit data to a receiver in which one or more illustrativeembodiments of the invention may be implemented.

FIG. 11 is a flowchart illustrating an example of a method oftransmitting data and/or FEC packets in a data block in which one ormore illustrative embodiments of the invention may be implemented.

FIG. 13 is a flowchart illustrating one example of obtaining oradjusting window granularity in which one or more illustrativeembodiments of the invention may be implemented.

FIG. 14 is a flowchart illustrating another example of obtaining oradjusting window granularity in which one or more illustrativeembodiments of the invention may be implemented.

FIG. 15 is a flowchart illustrating an example of the transmission ofreactive FEC packets in which one or more illustrative embodiments ofthe invention may be implemented.

FIG. 16 is a flowchart illustrating an example of a method of decodingat a receiver in which one or more illustrative embodiments of theinvention may be implemented.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the various embodiments, reference ismade to the accompanying drawings, which form a part hereof, and inwhich is shown by way of illustration various embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural and functional modificationsmay be made without departing from the scope and spirit of the presentinvention.

FIG. 1 illustrates an example of a communication system in which thepresent invention may be implemented. In this example, data may becommunicated over wireless channels. For example, data may betransmitted from a user device such as a telephone 101, a laptopcomputer 102, a desktop computer 103, or any other device capable oftransmitting data. In one example, devices at a customer premise such asa home, business or hotspot, may communicate data via an internal accesspoint 105. In the example illustrated, a laptop computer 102communicates via a wireless connection 109 with an access point 105 atthe customer premise. Likewise, a desktop computer 103 communicates viaan Ethernet connection 108 with the access point 105. The access point105 in this example may also communicate with a subscriber station 104.

As FIG. 1 illustrates, the subscriber station 104 may transmit orreceive data via a wireless connection with a base station 106. Thewireless station may be any variety of wireless channels. Some examplesof wireless channels include WiFi, WiMAX, 3G, mesh networks, communitywireless networks, satellite networks, or other wireless channels fordata communication including end-to-end communication involvingtraversal of multiple wireless links, to name a few. The base station106 may further communicate, for example through a fiber network, with anetwork such as the internet 107.

A transport protocol may be used as a transport layer for datacommunication over wireless channels. The present invention may beapplicable to any transport layer protocol including, for example,Transport Control Protocol (TCP) or any non-TCP transport protocol suchas multimedia streaming via RTP over UDP, custom transport protocols(e.g., NASA's satellite networks), signaling protocols such as SCTP,etc. The present description will refer to TCP as one example of atransport layer protocol in the present invention. However, it isunderstood that any transport protocol may be used.

TCP usually responds to congestion in the network by reducing thecongestion window in response to a loss of packet data. For example, ifcongestion occurs, data may be stored in a buffer for later transmissionat a time when congestion eases. Thus, when congestion is present, TCPmay respond by estimating a lower capacity of the network and reducingthe congestion window accordingly. FIGS. 2A-2C illustrate an example ofTCP performance during congestion in a communication network. FIG. 2Aillustrates a transmitter 130 that transmits data to a receiver 131. Thedata being transmitted is in the form of data packets 133 that may betransmitted over a channel at a particular bandwidth capacity 132. Datapackets may also be referred to as data segments. FIG. 2B illustratesdata communication in one example in which there is congestion in thenetwork. In this example, the transmitter 130 transmits data packets 133to receiver 131. However, due to the presence of congestion, datapackets are lost in the network. The receiver 131 receives the datapackets 133 and sends an acknowledgement (ACK) or selective ACK (SACK)to the transmitter via a feedback loop 136. In this example, datapackets have been lost due to congestion. Based on the data packet loss,TCP estimates a lower capacity of the network and adjusts the window toaccommodate for the estimated lower capacity due to congestion. Theadjusted window 134 reduces the amount of traffic sent into the networkper unit time (has diminished bandwidth demand) as compared to theoriginal window 132. Hence based on the loss feedback from the receiver131, the capacity of the network is assumed to have been reduced and thebandwidth demand on the network by the end system is correspondinglydecreased.

FIG. 2C illustrates an example of the present invention in which atransmitter 130 transmits data packets 133 to a receiver 131. Despitethe potential loss of data packets due to packet corruption, datapackets are transmitted to the receiver 131 at near capacity. Asillustrated in this example, the bandwidth capacity of the network 135is similar to the bandwidth capacity in the absence of congestion 132.The transport layer used in this example is the Loss TolerantTransmission Control Protocol (LT-TCP) as described herein.

FIG. 3 is a diagram illustrating an example in which the LT-TCP mayinclude any number of elements. In this example, LT-TCP includes anadaptive maximum segment size (MSS) 122 in which the segment size may belimited, adjusted or otherwise adapted. In one example, the granulationof the congestion window is adjusted to have a number of data packetssubject to a predetermined minimum or maximum number. Also, LT-TCP mayfurther include proactive Forward Error Correction (FEC) 120 and/orreactive FEC 121. In calculation of proactive FEC packets, a determinednumber of FEC packets may be provided proactively prior to transmission.In one example, redundancy is added to the data such that bit errors orpacket erasures on the channel are tolerated. Reactive FEC 121 mayprotect original transmission or retransmissions of TCP as furtherdescribed below.

FIGS. 4A and 4B illustrate an example of transmission loss during datacommunication. FIG. 4A is a general diagram illustrating thetransmission of data packets. In the example illustrated, data packetsare transmitted from a sender to a receiver. The packets are received atthe receiver which responds by transmitting a status to the sender ortransmitter. For example, the status may be an acknowledgement (ACK)that the data packets were received successfully at the receiver. Inaddition, a plurality of data packets may be acknowledged via selectiveACK (SACK) to indicate that some data packets are received while othermay not have been received. As one example for illustration purposes, ifSACK has a value of: 1110011101, then packets 1, 2, 3, 6, 7, 8, and 10were received while packets 4, 5, and 9 were not. For example, the SACKmay indicate the beginning and end of consecutive bytes that have beenreceived correctly. After the data packets are transmitted from thesender, the sender may wait a designated length of time during a timeoutperiod. The timeout as used in this example is the amount of time thesender waits while expecting the receipt of an acknowledgement (e.g.,SACK) from a receiver indicating that the data packets transmitted werereceived at the receiver intact. If an acknowledgement of a data packetis not received within the allotted timeout period, the transmitted datapacket may have been lost. Thus, packet loss may be detected by failureto receive an ACK at the sender from the receiver within the timeoutperiod. In this case, the sender or transmitter may re-transmit themissing data packet. For example, the sender may transmit repair datapackets to the receiver.

Another way of detecting data packet loss is through the use ofduplicate acknowledgements (dupacks). A dupack may be used toacknowledge a previously received data packet in which an ACK has beenpreviously provided. For example, if a first data packet is received ata receiver from a sender, the receiver may transmit an ACK to the senderto indicate receipt of the first data packet. However, if the nextexpected second data packet is not received at the receiver, then thereceiver does not send an ACK for the second data packet. If the sendertransmits and the receiver receives a third data packet, the receivernot having received the second data packet, sends an ACK for the firstdata packet (i.e., the last data packet that the receiver successfullyreceived). In this case, the second ACK indicating receipt of the firstdata packet is a duplicate ACK (i.e., dupack) because the dupackre-acknowledges the receipt of the first data packet which waspreviously indicated. Thus, the receiver may indicate through the use ofdupacks that a particular data packet was not received after subsequentdata packets are transmitted (i.e., it is a duplicate of a previousACK). In addition, the dupack may also indicate that a new packet thatwas out of sequence was received at the receiver. Traditionally, a TCPsender retransmits a packet only when a third dupack is received fromthe receiver.

FIG. 4B illustrates an example of total loss of data packets in a windowthat has low window granularity. In this example, the maximum segmentsize (MSS) is large as each segment or packet within the window islarge. This results in low window granularity. As illustrated in thisexample, the window contains five (5) data packets, data packets 1-5.However, due to a variety of reasons, such as, for example, weatherconditions or interference over a wireless link that may be part of theend-to-end network, data packets may be lost during transmission.Because the window of this example has low window granularity (i.e.,segments or packets in the window have a high MSS), it is more likelythat data packet loss may occur. This is because the larger the maximumsegment size, the more likely that total loss of the data packet mayoccur. In addition, the length of time the impairment in transmission ispresent on the link (e.g., weather conditions on a wireless link), themore likely that all the data packets in the window are lost. In theexample illustrated in FIG. 4B, window granularity is low and all datapackets in the window are lost. Hence, the receiver does not return anACK to the sender and timeout thus occurs at the sender. Typically, aTCP sender responds to a timeout by reducing the window size drastically(e.g., to 1 or 2 packets) and then gradually builds the window back upas packets are successfully transmitted.

In one example of the present invention, a transport protocol, such asbut not limited to TCP, treats data packet loss as congestion if anExplicit Congestion Notification signal (ECN) is present in anECN-capable network path such that an ECN may be generated whencongestion is detected locally. Conversely, if an ECN signal is notpresent in an ECN-capable network path, then the transport protocol doesnot treat data packet loss as congestion. In this example, a transportprotocol (e.g., Loss Tolerant TCP (LT-TCP)) may respond to congestion ina communication network by altering its sending rate or window when anindication, such as the ECN signal, is received that indicates that thenetwork is congested as opposed to data packets being lost for otherreasons (such as data loss in a lossy system or packet erasures). Inthis example, the Explicit Congestion Notification (ECN) may begenerated by the network based on the state of the queue in order toindicate congestion in the network. For example, data packets may bemarked during congestion in the network by routers in the network byinserting an ECN signal in the header to indicate to the network thatcongestion exists. Receivers that receive marked data packets may returninformation regarding the marked data packets and the senders maydecrease the transmission rate accordingly. In this case, the transportprotocol such as LT-TCP may respond to the congestion because itreceives an unambiguous indication of congestion through the ECN marks.

However, when there are no ECN indications received at the receiver, theloss of data packets is not considered to be due to congestion. In thisexample, other packets successfully received are also not marked withthe ECN mark indicating congestion. Therefore, LT-TCP does not respondto congestion but instead treats the packet losses as being due toerrors in the network to provide a loss-tolerance response. Theloss-tolerance response is further described herein.

In one example of the loss-tolerance response of the transport layerprotocol of the present invention in response to network congestion, themaximum segment size and the number of data packets or segments in awindow may be adjusted to increase window granulation. FIGS. 5A and 5Billustrate the effects of window granularity on timeout andre-transmission of data packets. FIG. 5A illustrates an example of awindow (W) 501 of five (5) data packets: data packet 1 (502), datapacket 2 (503), data packet 3 (504), data packet 4 (505) and data packet5 (506). Each of the five data packets (502-506) in the window 501 aretransmitted sequentially over the network from a sender to a receiver.However, due to various conditions on the network (e.g., interference orweather conditions, for example), only data packet 1 502 and data packet5 (506) are successfully received at the receiver. Data packets 2-4(503-505) are not received and are thus lost. Hence, when data packet 1(502) is received at the receiver, the receiver returns an ACK (i.e., 1ACK 507) to the sender to indicate that data packet 1 (502) wassuccessfully received at the receiver. However, an ACK is not returnedfor each of data packets 24 (503-505) because data packets 24 (503-505)are not received. When data packet 5 (506) is transmitted from thesender and received at the receiver, the receiver receives the datapacket 5 (506), however, because none of data packets 2-4 (503-505) weresuccessfully received at the receiver, the receiver responds to thereceipt of data packet 5 (506) by returning a dupack (508) to thesender. The dupack indicates to the sender that data packets were lostand that the last successfully received data packet was data packet 1(502). Similarly the packet sent in response to 1 ACK 507, i.e. datapacket 6 (not shown) generates a second dupack. However, in the exampleof FIG. 5A, the window granularity is low (i.e., the size of each datapacket or segment is large) and no further dupacks are generated becauseno further out-of-sequence data packets are allowed in the window. Inthis example, there are an insufficient number of dupacks received andonly one dupack is received at the sender in response to the receptionof data packet 5 at the receiver. Therefore, the sender times out whilewaiting for an ACK on packet 2. Also, there are no other dupacksreceived. Therefore, an excessive amount of time elapses after theinitial ACK responsive to the receipt of data packet 1 (502) wasreceived at the sender. Thus, the sender undergoes timeout to retransmitall the packets starting with data packet 2. Timeout wastes capacity andleads to lower performance.

FIG. 5B illustrates the effect of increased window granularity ontransmission of data packets. In this example, as compared to theexample illustrated in FIG. 5A, the maximum segment size (MSS) isadjusted such that the size of each of the data fragments or segmentswithin the window is decreased (i.e., window granularity or the numberof data packets or segments in the window is increased). In the examplesillustrated in FIGS. 5A and 5B, the total number of data bytes in thewindow is still the same in FIG. 5A and FIG. 5B. In this example, thewindow (W) 501 includes eight data packets—data packets 1-8 (509-515,519). The eight data packets 1-8 (509-515, 519) are transmittedsequentially over the network from the sender to the receiver. However,due to conditions such as weather conditions or interference, only datapackets 1 (509), 2 (510) and 6-8 (514, 515, and 519) are successfullyreceived at the receiver. Data packets 3-5 (511-513) are lost intransmission. The channel conditions that cause bit errors have asmaller multiplier effect in terms of number of packet losses becausethe MSS is now smaller.

The receiver returns an ACK for each successfully received data packetor segment. Hence, in the example illustrated in FIG. 5B, the receiverreceives data packet 1 (509) and responds by returning ACK 1 (516). Thereceiver then receives data packet 2 (510) and responds by returning ACK2 (517). However, because data packets 3-5 (511-513) are each notreceived at the receiver, the receiver does not return an ACK for any ofdata packets 3-5 (511-513). Data packets 6-8 (514, 515, 519) are thentransmitted from the sender to the receiver. Because in this example thereceiver successfully receives data packets 6-8 (514, 515, 519) and notdata packets 3-5 (511-513), the receiver responds by returning 3duplicate acknowledgements (dupacks) for packet 2 (518, 520, 521) whenit receives packets 6, 7 and 8 (514, 515, 519). However, because none ofdata packets 3-5 (511-513) were received at the receiver, the receiverresponds to the receipt of data packets 6-8 (514, 515, 519) by returninga dupacks 518, 520, and 521 corresponding to data packet or segment 2(510) upon reception of each of packets 6, 7 and 8 (514, 515, 519). Thedupacks (518, 520, 521) indicate that data packets have been lost andthat the last received data packet or segment at the receiver was datapacket 2 510 in this example. The additional 3 dupacks (518, 520, 521)are received at the sender. This causes the sender to retransmit packet3.

Also in the example of FIG. 5B, the window granularity is high (i.e.,the number of data segments or packets in the window is high and thesize of each of the data packets in the window is small). Therefore, thesender, not having received an ACK for any of data packets 3-5(511-513), has still not undergone timeout when the three dupacks 518,520, 521 are received indicating data packet or segment loss in thenetwork. As a result, the sender is able to re-transmit the lost datapackets 3-5 (511-513) to the receiver. Thus, in the example illustratedin FIG. 5B, increased window granularity prevents timeout and permitssuccessful transmission and re-transmission of data packets or segments.

In another example, Forward Error Correction (FEC) packets may be usedto reconstruct lost data packets. FEC packets may be proactive orreactive. Proactive FEC packets may be created to provide adequateprotection against data packet erasure. In one example of proactive FECpackets, a determined number of proactive FEC packets are added to andtransmitted in a window with the data packets. The Maximum Segment Size(MSS), which may be subject to minimum and/or maximum values, may alsobe adjusted or adapted as described herein to provide a proper windowgranularity as well as to accommodate the FEC packets transmitted withthe data packets. Thus, in this example, data packets or segments aretransmitted in a window of data packets with a number of FEC packets andthe MSS may also be adjusted or adapted to accommodate the FEC packetsand/or maintain a desired window granularity.

FIG. 6 illustrates an example of recovery of FEC data packets. In thisexample, a window of packets 601 with a block size of N is transmittedin a data communication network. The N packets 601 include K (where K<N)data packets 602 and P FEC packets 603, where the sum of K data packets602 and P FEC packets 603 is N packets 601. The communication network ofthis example may be a lossy system in which data packets are lost duringtransmission. In this example, a total of K packets 607 are received.Some of the packets 607 received are the original data packets 602whereas the other packets received may be any of the FEC packets 605.Error correction packets (i.e., FEC packets) in this example permit FECreconstruction of lost packets. Thus, in this example, it does notmatter which data packets are received. An FEC packet (e.g., any one ofpackets 603) may protect or repair any data packet (e.g., any of datapackets 602). Hence, missing data packets 602 (i.e., data packets 608)may be reconstructed with FEC packets received (i.e., data packets 605).This results in K data packets recovered (i.e., data packets 606).

There are many other examples of alternative methods of generating FECpackets. For example, one additional method is to precompute aninventory of FEC packets used for proactive and/or reactive FEC, and usea set of zero-segments to complete a “block” used in traditionalblock-based FEC encoders. Either Reed-Solomon (RS) codes or otherblock-based codes can be used. Another method is to compute new FECpackets on the fly as needed for the segments. Any of the class ofrandomized low-density parity check (LDPC) codes that can be used. Inany case the “sequence-agnostic” property of FEC may be used toreconstruct the window because the order does not matter. Also, thetransport layer can deliver in-order data segments to the applicationeven as it waits for more FEC packets to reconstruct the block.

In addition to proactive FEC packets, FEC packets may also be reactive.Reactive FEC packets may be provided and transmitted in response to datapacket loss. For example, reactive FEC packets may be used in responseto dupacks from a receiver. FIG. 7 illustrates an example of a block ofdata packets including proactive and reactive FEC packets. As FIG. 7illustrates, a Window (W) 701 contains data packets which includesproactive FEC (F) packets 702 and data packets 703 which may betransmitted from a sender to a receiver. However, if data packets arelost during transmission, the receiver fails to receive all of thetransmitted data packets and the transmitter does not receive acorresponding ACK from the receiver. In response, the transmitter maytransmit a corresponding number of reactive FEC packets 704 to thereceiver. Hence, reactive FEC data packets may complement and protectretransmissions that are sent in response to SACKs. The reactive FECpackets may serve to repair the original transmissions or theretransmissions that are lost.

FIG. 8 illustrates an example of proactive FEC data packets in atransmission. In this example, a window (W) of data packets containsfour data packets 801 (data packets 1-4) and two proactive FEC packets802. During transmission, however, data packets 3 and 4 are lost. Thismay be due to, for example, interference or weather conditions. However,proactive FEC packets 802 are successfully transmitted. Hence, the twotransmitted proactive FEC packets 802 are used to reconstruct the lostdata packets. This results in successful transmission of all of the datapackets (i.e., data packets 14 in this example) without the use ofdupacks.

FIG. 9 illustrates an example of re-transmission of lost data packets.In this example, a window of data packets contains six data packets(i.e., data packets 1-6). However, during transmission, some datapackets may be lost. In this example, data packets 2 and 3 are lostduring transmission. Hence, a receiver may receive data packet 1 butfail to receive data packets 2 and 3. In this example, the receiversends an ACK to the transmitter responsive to receiving data packet 1.However, data packets 2 and 3 are not received at the receiver in thisexample. Thus, the receiver does not return an ACK for either of datapackets 2 or 3. When data packet 4 is received at the receiver, thereceiver has not received data packets 2 or 3. Therefore, the receiverreturns a dupack responsive to receiving data packet 4. The dupackindicates that data packet loss has occurred and that the lastsuccessfully receive data packet was data packet 1. In addition, thereceiver may further send the dupack in response to each data packetsubsequently transmitted by the transmitter and received by the receiveruntil a retransmission of data packet 2 is received. As illustrated inFIG. 9, three dupacks are returned in the ACK stream to the transmitter,responsive to receiving data packets 4, 5, and 6, respectively. Thetransmitter retransmits data packet 2 to the receiver responsive to thedupacks and the receiver may acknowledge the retransmitted data packet 2by sending a corresponding ACK.

However, in many cases, the retransmitted data packet may itself be lostduring transmission. In this example, if retransmitted data packet 2 isalso lost before being successfully received at the receiver, thereceiver may continue to transmit dupacks to the transmitter until thetransport protocol undergoes timeout. During the timeout period, nopackets are transmitted by the sender, and data packet 2 will beretransmitted at the end of the timeout period. The timeout period canbe substantial, and can thus result in a significant loss of throughput.

FIG. 10 illustrates an example in which reactive FEC packets may be usedin the transmission of data to a receiver. In this example, a window (W)of data packets contains six data packets (data packets 1-6). Duringtransmission of the window of data packets, data packets 2 and 3 arelost (in this example). The receiver receives data packet 1 from thetransmitter and acknowledges receipt of the data packet by returning anACK corresponding to data packet 1. However, data packets 2 and 3 arenot successfully received at the receiver. Therefore, the receiver doesnot return an ACK in acknowledgement of data packets 2 or 3. Instead,the receiver returns dupacks for subsequently transmitted (and received)data packets, such as 4, 5 and 6.

In response to receiving dupacks from the receiver, the transmittertransmits reactive FEC packets to reconstruct the lost data packets(i.e, data packets 2 and 3 in this example). As illustrated in FIG. 10,two reactive FEC packets are transmitted from the sender or transmitterto the receiver. The receiver may receive the reactive FEC packets whichmay be used at the receiver to reconstruct data packets 2 and 3. Asshown in FIG. 10, the receiver uses the reactive FEC packets forreconstruction of data packets 2 and 3 to obtain all of the transmitteddata packets (illustrated as data packets 1-4 in FIG. 10). The abilityto use the reactive FEC packets to repair the loss of any of the lostpackets enables efficient recovery.

Thus, in one example of the present invention, LT-TCP may respond tocongestion in a communication network by altering the sending rate whenan indication is received that the network is congested. In one example,the network congestion is indicated based on the state of the queue inwhich an Explicit Congestion Notification (ECN) is generated by thenetwork and inserted into a data packet (e.g., in the header of the datapacket) to mark the data packet. The marking may be accomplished, forexample, by routers in the network. In this case, the transport protocolmay respond to the congestion because it receives an unambiguousindication of congestion through the ECN marks. Conversely, if there arelost data packets but no ECN indications received at the receiver, theloss of data packets is not due to congestion. Therefore, LT-TCP doesnot respond to congestion but instead treats the packet losses as beingdue to errors in the network.

When the transport protocol identifies congestion in the network (e.g.,an ECN indication is present), the transport protocol may further adjustor adapt the MSS. In one example, the transport protocol adapts the MSSby reducing the MSS to thereby increase the window granularity. Forexample, the MSS may be decreased by some factor (e.g., factor “f”), forexample, between 0% and 100%. In another example, the factor “f” is 50%such that MSS is decreased by ½.

The transport protocol may respond to packet loss/erasure by providingproactive FEC packets. The FEC packets increase reliability and may beprovided in anticipation of losses in a window. The FEC packets thusprovide an “insurance” against packet loss. The number of proactive FECpackets may be based on an adaptive estimate of erasure rate. Forexample, the transport protocol may estimate an erasure rate per windowof data packets. Based on the estimated data packet erasure rate perwindow, the transport protocol may adjust the MSS to allow proactive FECdata packets while maintaining sufficient window granulation.

The erasure rate may be estimated in a variety of ways. In one example,an estimate of the packet erasure rate may be determined based on anexponential weighted moving average (EWMA). For example, the EWMAparameters may be adaptively biased toward higher erasure rates. Forexample, ifN=new measured erasure rate;α−(N)/(N*E);β=1−α=(E)/(N+E),

then the estimated erasure rate may be determined in this examplethrough an averaging process as follows:E=estimated erasure rate=a*N+β*E

In another example, values of α and β may be constant (i.e., no bias).For example, in another example, α and β may be set to a constant valuesuch as 0.5.

A function is provided for mapping an estimate of a data packet erasurerate to a number of proactive FEC data packets to be added to the windowof data packets for a window size in bytes. In this example, an estimateof an erasure rate is obtained, and the number of FEC packets in thenext block may be computed based on the estimate. For example, given acertain window size in bytes (e.g., W) and the current estimated loss,these may be used to determine the amount of protection for the block.As one example to illustrate, if the estimated loss rate is 10%, then10% of the packets are to be proactive FEC packets. The remainingpackets are data packets. The sender may then determine the proactiveFEC packets in bytes as equal to W*estimated erasure rate, where W isthe window size in bytes. Also, the number of data packets may bedetermined as equal to W*(1−estimated erasure rate) resulting in a splitbetween the bytes corresponding to data and bytes corresponding toproactive FEC in the block. Based on the number of bytes of data andFEC, respectively, the number of data packets or segments and proactiveFEC packets or segments can be determined as the number of proactive FECpackets (“P”) being the bytes of proactive FEC divided by the currentMSS. The number of data packets or segments (“K”) may be determined asthe number of bytes of data divided by the current MSS. K+P make up theentire block of “N” packets.

Thus, in an example of the present invention, a window size is initiallydetermined based on congestion control algorithms or mechanisms. Thismay be based on, for example the end-system's estimate of its fair shareof the network capacity. The MSS may then be determined based on thewindow size and a desired (or minimum) window granularity. In addition,proactive FEC packets may be added to a number of data packets in thewindow. The number of proactive FEC packets added to the data packets inthe window may be determined, for example, based on an estimated erasurerate. In addition, the MSS may be adapted or adjusted to accommodate theproactive FEC packets and to maintain a desired minimum windowgranularity given the window size. A window of packets may then betransmitted via the network to a receiver, the window of packetscontaining a number of data packets and a number of proactive FECpackets. In addition, a number of reactive FEC packets may also beprovided based on the dynamic state as currently observed and/or thenumber of packet erasures observed in the last SACK received at thesender. For example, when the receiver decodes a block, it knows whichpackets made it through and which did not. Variables may be maintainedthat determine how many packets (data or FEC) are needed before thisblock can be completely decoded. This number may be fed back as the“hole size.” The number of reactive FEC packets is determined by the‘hole sizes’ in the ACKs. For example, the count of proactive FECpackets sent for the block, reactive FEC packets sent for the block andSACK retransmissions may be used to limit the number of reactive packetsgenerated. Otherwise, the sender will send a certain number of reactivepackets so that these will cover the holes for the estimated error rate.

FIG. 11 is a flowchart illustrating an example of a method oftransmitting data and/or FEC packets in a data block. In this example,an ECN signal is detected (STEP 1101). The ECN signal indicates thatthere is congestion in the network. In this example, MSS adaptation andFEC provisioning in each window may be achieved independently of ECN.For example, the window can increase when no ECN is received during MSSadaptation, proactive FEC provisioning, and/or reactive FEC response todupacks. ECN signal may also cause a decrease in the window by a factorof ½, for example and/or a decrease in the MSS by a factor f. Therefore,the transport protocol processes the MSS and FEC packets based on thepresence of congestion in the network. In STEP 1102, a loss estimate isdetermined. Also, the window size is obtained in STEP 1103. Based on thewindow size obtained in STEP 1103 and the loss estimate determined inSTEP 1102, a number and/or proportion of proactive FEC packets isdetermined. This number of proactive FEC packets may be determined inrelation to the number of data packets based on, for example, the lossestimate obtained in STEP 1102. The loss estimate obtained in STEP 1102may also be used to determine window granulation. The window sizeobtained in step 1103 and the loss estimate obtained in STEP 1102 mayalso be used to determine a window granulation (i.e., the number ofpackets or segments in the window) (STEP 1104). Based on the lossestimate, the window size and window granulation, the MSS may be adapted(STEP 1105). The data window is transmitted in the network (STEP 1106)at the determined window granularity and containing the calculated ratioof proactive FEC packets to data packets.

In another example of the present invention as illustrated in FIG. 12, ablock of packets is created. In this example, a loss-estimate isinitially set to “0” (STEP 1201) and a window is initially set with aminimum window granularity (“G”) (STEP 1202). The loss-estimate may besubsequently adjusted accordingly when an ACK is received. G describesthe minimum number of packets or segments in the window and may be setto any value. In one example, G is set to 10. Each of the at least Gpackets or segments in the window may contain a number of bytes whichmay be between a minimum (“minmss”) and a maximum (“mssmax”) number. Inone example, minmss is 200 bytes and max mss is 1500 bytes. Also, aparameter for the block number (“blocknumber”) is initially set to “1”to indicate the first block (STEP 1203). The blocknumber parameter isincremented for subsequent blocks.

In this example, the block size of the current block is set to the sizeof the window (“W”) (STEP 1204). Hence, the window size (“W”) is used asa guide to determine the block size. In one example, W is greater thanequal to 2000 bytes. The number of packets or segments within the blockis “N” (i.e., the total number of packets in the block). These N packetsin the block are split into a number of data packets (“K”) and a numberof proactive FEC packets (“P”) (STEP 1205). The number of proactive FECpackets (“P”) may be based on the estimated loss relative to the numberof data packets (“K”) in the block. As one example, if the loss isestimated to be 10%, then the number of proactive FEC packets (“P”) isset to about 10% of the total number of packets or segments. In oneexample, the initial estimate for proactive FEC packets is 50%. In thisexample, the first block may have 5 proactive FEC packets and 5 datapackets for a total number of 10 packets with an initial conservativeestimated loss rate of 50% (loss estimate is equal to the % of ProactiveFEC packets in this example). In this example, unused proactive FECpackets may be considered “overhead”. The overhead may be reduced withsubsequent loss-estimates.

The N packets in the block (including K data packets and P proactive FECpackets) are transmitted through the network (STEP 1206). Aftertransmission of the block, the values for K and P for the next block aredetermined (STEP 1207) based on the current value of loss-estimate andthe window size W. When an ACK is received from the receiver, the senderupdates the loss estimate accordingly (STEP 1208). This process maycontinue until the connection is terminated.

Block sizes may be determined by the current window size. Aftertransmission of a block is completed, the next block is created. In oneillustrative example, if the window slides (upon reception of ACKs) toallow the transmission of a packet not in any block, this triggers theformation of a new block. This may occur even if the current block istransmitted. In one example, if a packet/segment is retransmitted, theretransmitted packet/segment is still assigned to the same block numberas it was originally assigned. The state of blocks may be furthermaintained in a state table. Thus, a state table may be searched toobtain information on the state of any number of blocks.

A sender may operate in any number of modes. For example, a sender mayoperate in a data mode in which data packets are transmitted in theblock. Also, the sender may operate in a proactive FEC (PFEC) mode inwhich once K data packets are transmitted, the sender may transmitproactive FEC (PFEC) packets. After K+P packets are sent, a next blockis made. If a timeout or retransmission occurs, the system may freezethe state of the current block while older packets/segments are sent toensure that the right packet/segment is sent. Then the count for thecurrent block is not incremented. In addition, the sender may implementfast recovery when a third dupack is received. If duplicate ACKs arereceived, the sender may send a reactive FEC packet. In this example,the ACKS may contain hole sizes for different blocks—the blockcorresponding to the packet received last by the receiver and the blockcorresponding to the ACK number in the ACK field (could be an olderblock). The hole is the number of packets/segments still needed at thereceiver to fully reconstruct a block. The sender may send reactive FECpackets in response to hole size information fed back to the sender.

In an example of adjusting the window granularity, variables areestablished corresponding to a temporary size of packets (i.e.,“tmpsize”) and a maximum value for MSS (i.e., “maxmss”). FIG. 13 is aflowchart illustrating one example of obtaining or adjusting windowgranularity. In this example, the congestion window is obtained in bytes(e.g., “wndinbytes”) (STEP 1210). The number of segments or packetsaccommodated in the window (“tmpsegs”) is determined as the congestionwindow in bytes (“wndinbytes”) divided by the temporary size of packets(“tmpsize”) (STEP 1211). The tmpsize is compared to the minimum windowgranularity (“G”). If the tmpsize is less than or equal to the minimumwindow granularity (YES branch of step 1212), then the tmpsize isdecreased (STEP 1214) and tmpsegs is recalculated with the updatedtmpsize (STEP 1215). When tmpsize becomes less than or equal to G (NO ofstep 1212), then the values for trapsize and tmpsegs are output (STEP1213) as the size of segments and the number of segments, respectively.

FIG. 14 is a flowchart illustrating another example of obtaining oradjusting window granularity. In this example of adjusting the windowgranularity, the tmpsize variable is set to the current MSS value (STEP1220). Tmpsegs is determined as the congestion window in bytes(“wndinbyte”) divided by tmpsize (STEP 1221). The value of tmpsize isthen incremented by “stepvalue,” (STEP 1222) which describes the numberof bytes by which the MSS value can be increased in one pass. In oneexample, stepvalue is equal to about 200 bytes. The value of tmpsegs isthen recalculated with the updated tmpsize value (STEP 1223). If thenumber of segments (tmpsegs) is less than or equal to the minimum windowgranularity (G) (“YES” branch of STEP 1224) and the packet/segment size(tmpsize) is less than or equal to a maximum value for MSS (“maxmss”)(“YES” branch of STEP 1225), then the MSS is set to tmpsize and thenumber of packets or segments in the window is set to tmpsegs (STEP1227). Otherwise (“NO” branch of either STEP 1224 or STEP 1225), the MSSand the number of packets or segments in the window is not updated (STEP1226).

In another example of window increase behavior, an ECN is received(indicating the presence of congestion) and the packet/segment size isreduced accordingly. However, if the packet size becomes less than aminimum value for MSS (“MIN_MSS”), then the window size (in segments) iscut instead subject to a minimum window granularity. For example, thewindow size in bytes may be cut upon reception of the first ECN in awindow. In this example, the MSS adaptation policies affect the windowsize in units of segments but may not affect the bytes. During windowincrease, the window size in bytes may be determined and compared to apredetermined threshold in bytes to determine if the process is inslowstart. In one example, after a timeout, the window is resized to 10packets of 200 bytes. In another example, when an ECN is received, thewindow size in bytes may be cut in half which may be accomplished bycutting the packet size by half or the number of segments by half.

FIG. 15 is a flowchart illustrating an example of the transmission ofreactive FEC packets. In this example, a sender receives an ACK whichmay be a dupack from a receiver (STEP 1230). A hole size for the currentblock and for the last block in which a corresponding ACK was receivedmay be determined. These values may be updated in a state machine in thesender. If a dupack is received (STEP 1230), a reactive packet FECpacket may be sent (STEP 1234). In the transmission of a reactive FECpacket, a count of the number of proactive FECs, reactive FECs and/orSACK packets sent from the block is obtained (STEP 1231). The expectednumber of FEC or retransmissions may be calculated (STEP 1232). Thenumber of reactive packets to be sent from the current block may bedetermined (STEP 1237) from various factors. For example, the number ofreactive packets to be transmitted from the block may be based on thenumber of proactive FEC packets expected to reach the receiver. In thisexample, the number of proactive packets expected to reach the receivermay be estimated by subtracting a loss estimate from one and multiplyingby the number of proactive FEC packets sent from the block to obtain a“backed-off” PFEC value. The backed-off PFEC value may further be usedto determine the number of reactive FEC packets to be sent from thecurrent block.

In another example, the number of reactive FEC packets may be based onthe number of retransmissions expected to reach the receiver, i.e., thenumber of “backed-off” retransmits. In this example, the number ofretransmissions expected to reach the receiver may be estimated bydetermining a loss estimate, subtracting the loss estimate from 1 andmultiplying by the number of retransmissions sent. Hence, the number ofreactive FEC packets to send from the current block may be estimatedbased on a function of any of a variety of variables such as but notlimited to the backed-off PFEC, the backed-off retransmits, or any oneor combination of other variables such as the total number of packets ina block, the number of data packets in the block, the number ofproactive FEC packets in a block, or the number of reactive packets sentfrom the block.

If the total number of reactive FECs (“R”) is less than or equal to thenumber of reactive FEC packets to be sent from the block (“YES” branchof STEP 1233), then a reactive packet is sent from the current block(STEP 1234) and the number of reactive FEC packets sent from the currentblock is updated in view of the loss rate (STEP 1235). Thus, theexpected number of FEC and retransmissions that have reached thereceiver is calculated.

Each ACK received from the receiver may contain information on the holesizes of a block corresponding to the current incoming packet (the“current” block) and a block corresponding to the block for which thecumulative ACK is being sent (the “last” block). As one example, areceiver awaits packet number 212 from block 10 block 11 has been fullydecoded and packet number 243 from block 12 is the next packet. The holesize for block 10 is 2, for example, and the hole size for block 12 is0, for example. Thus, in this example, the ACK from the receivercontains information on the hole size of 2 for block 10 and the holesize of 0 for block 12.

When the sender receives the ACK, it may check a “phase3 flag” in thepacket which is set on all reactive FEC packets from the sender. ThePhase 3 flag may be set in the header and may be echoed back and triggerfurther reactive FEC packets. When the sender identifies the phase3flag, the sender sends a reactive FEC packet. This ensures a steadystream of packets. When a dupack is detected, reactive FEC packets maybe sent from the “current” block and the “last” block as needed, basedon the indication in the SACK-based acknowledgements received at thesender. The number of react packets thus sent is determined based onvarious factors. For example, the sender may first estimate the numberof proactive FEC packets expected to have reached the receiver. Thisvalue may be set to 0 or may be determined using the loss estimate(e.g., expected proactive FECs=(1−loss rate)*pfec_sent).

The sender may know the number of SACK retransmissions received so far,the number of reactive FEC packets sent so far from the block, and thehole size for the block. The hole size may be cumulative (i.e., may notdecrease) to avoid accounting for holes filled by retransmissions orhole sizes that increase or decrease. Once the SACK retransmissions andPFEC packets are “backed off”, the sender sends enough react packets tofill the hole size. This may also account for the loss estimate. Forexample, if after backing off, 5 holes have to be filled and the lossestimate is 50%, then 10 packets will be sent. Thus, the receiver mayknow the number of retransmissions and original transmission it hasreceived. In another example, the receiver may know the number ofretransmissions sent from the sender.

FIG. 16 is a flowchart illustrating an example of a method of decodingat a receiver in the present invention. In this example, an incomingpacket (STEP 1240) belonging to a block is discarded (STEP 1246) and theprocess terminated (STEP 1255) if the incoming packet is for a blockalready decoded (“YES” branch of STEP 1241). If the packet belongs to anas yet undecoded block (“NO” branch of STEP 1241), then the structuresfor the block are initialized and allocated (STEP 1248) if the block hasnot been seen before (“YES” branch of STEP 1242). The incoming packetmay be processed based on the type of packet. If the packet is a TCPtype packet (“YES” branch of STEP 1243), then the packet is insertedinto a list of packets for the block and the list of packets ismaintained in sequence (STEP 1249). An ACK for the TCP packet is thensent/received (STEP 1250). If the packet is a FEC type packet (“YES”branch of step 1245), then the packet is saved along with other packetsfrom the block for decoding (STEP 1244) and an ACK is sent for the FECpacket received (STEP 1247). If K out of N packets from the block havebeen obtained (“YES” branch of STEP 1251), then the entire block isdecoded (STEP 1252) which may also reconstruct any missing packets withFEC packets received for that block. The new data packets may be furtherprocessed according to the transport protocol (STEP 1253). Thus, in thisexample, an ACK for the FEC packet indicates that the ACK for the lastdata packet is sent since FEC packets in this example do not havesequence numbers.

In the following example, a loss estimate is determined. In thisexample, a first proactive FEC packet is received and sample lossestimate is used to update the average loss estimate. One example ofdetermining the loss sample for each block includes obtaining the totalnumber of packets in the block and the total number of originaltransmissions that are present in the receiver decoding block (may beobtained by walking the list and checking the orig_trans flag in theheader). The number of lost packets is determined as the total number ofpackets minus the number of original packets. The loss sample may bedetermined as the number of lost packets divided by the total number oforiginal transmissions present in the receiver decoding block. The newloss estimate is determined using the EWMA equation where αand β=0.5.The loss estimate may then be echoed back in the ACKS from the receiverto the sender.

In the following example, hole size for blocks is determined. In thisexample, a packet is received and a number of packets that should havecome in for the corresponding block is determined. As one example, ifthe block starts at 100 and the highest packet in the block is 105, then6 packets should have been received in the block. In one example, thenumber of packets in the original transmission may be counted. In analternative example, the number of packets in the block, including theoriginal transmission and retransmission, is determined. In thisexample, the hole size is determined based on the difference between the2 numbers. The hole size is stored in the receiver decoding structureand the structure is accessed and the hole sizes for the last andcurrent blocks may be added to the ACK. This determination also appliesto FEC packets however, the total number of packets is the same. Forexample, the sender may start with a window of 10 and follow the basicself-clocking behavior for data and proactive FEC packets. In anotherexample, the hole size is not the difference between the original andretransmitted packets such that if the block starts at 100 and we have100, 102 and 103 which are original transmissions, and we have received109 and 110, of which 109 was a retransmission and 110 was original, wehave a hole size of 5 packets (104-108). In one example, theretransmitted packet 109 is ignored and the hole size is 6. By ignoringthe retransmitted packet, we inflate the hole size to send more reactpackets.

The following is another example of a sender proactive FEC algorithmwhere G is the minimum window granularity, MSS_(MAX) is the maximum MSSallowed, new, is the new measured erasure rate, P is the number of PFECpackets in the block, MSS1 is a temporary variable, MSS_(MIN) is theminimum MSS allowed, MSS is the current MSS used, E is the Averageerasure rate estimate, R is the number of RFEC packets in the block andW is the congestion window in packets. P=f(E) MSS_1 = (W*MSS*E)/P IF(MSS_1 < MSS_(MIN))   W = (W*MSS)/ MSS_(MIN)   MSS= MSS_(MIN)   IF((W*E)< 1)     R=1   ELSE     R = W*E ELSE   IF(MSS_1 > MSS_(MAX))     IF(W/MSSMAZ>G)       W=(W*MSS)/ MSS_(MAX)       MSS= MSS_(MAX)       R=W*E    ELSE       W=G       MSS=W/G       R=W*E     ELSE       IF(W/MSS_1>G        W=(W*MSS)/MSS_1         MSS=MSS_1         R=P       ELSE        W=G         MSS=W/G         R=W*E

The following is an example of a receiver FEC decoder method: IF(DataPacket)   IF (Next in Sequence)     IF (No Previous Unprocessed SavedPackets in the Block)       Process SACK Packet     ELSE       IF(Packet in Current Block) AND (Lost Packets <P))         Save the packet      ELSE         Process all Saved SACK Packets   ELSE     IF ((Packetin Current Block) AND (Lost Packets <P))       Save the Packet     ELSE      Process all Saved SACK Packets ELSE //Redundancy Packet   IF(AnySaved Packets)     IF ((Packet in Current Block) AND (Lost Packets <P))      Recover and Process all SACK Packets     ELSE       IF ((LastPacket in Block) OR (Packet in a New Block))         Process all SavedSACK Packets       ELSE

Save the Packet

The present invention includes any novel feature or combination offeatures disclosed herein either explicitly or any generalizationthereof. While the invention has been described with respect to specificexamples including presently preferred modes of carrying out theinvention, those skilled in the art will appreciate that there arenumerous variations and permutations of the above described systems andtechniques. Thus, the spirit and scope of the invention should beconstrued broadly as set forth in the appended claims.

1. A method for transmitting a data window containing packets in acommunication network, the data window having a window size, the methodcomprising the steps of: estimating a packet erasure rate; determining anumber of proactive FEC packets for the data window based on theestimated packet erasure rate; determining a packet size for the packetsin the data window based on the window size of the data window and thedetermined number of proactive FEC packets; transmitting the datawindow, wherein the packets in the transmitted data window have a sizecorresponding to the determined packet size and include the determinednumber of proactive FEC packets.
 2. The method of claim 1 wherein thestep of estimating a packet erasure rate comprises applying anexponential weighted moving average.
 3. The method of claim 1 whereinthe step of determining a packet size comprises determining granularityof the window.
 4. The method of claim 1 wherein the step of determininga packet size comprises decreasing the packet size for the data packetsby a factor f.
 5. The method of claim 4 further comprising receiving anExplicit Congestion Notification (ECN), wherein decreasing the packetsize for the data packet is responsive to the ECN.
 6. The method ofclaim 1 wherein the transmitted data window contains N data packets andwherein the N is equal to the sum of the number of data packets and thenumber of determined proactive FEC packets.
 7. The method of claim 6wherein N is determined based on the determined packet size.
 8. Themethod of claim 7 wherein N is further determined based on the windowsize.
 9. The method of claim 1 wherein the step of determining a numberof proactive FEC packets comprises setting the number of proactive FECpackets substantially equal to the estimated packet erasure rate. 10.The method of claim 1 wherein the step of determining a number ofproactive FEC packets comprises obtaining an amount of proactive FECbytes in the data window as the product of the window size and theestimated packet erasure rate; and, determining the number of proactiveFEC packets as the amount of proactive FEC bytes divided by a currentpacket size.
 11. The method of claim 10 further comprising determining anumber of data packets by: obtaining the amount of data bytes in thedata window as the product of the window size and the difference between1 and the estimated packet erasure rate; and, determining the number ofdata packets as the amount of data bytes in the data window divided bythe current packet size.
 12. The method of claim 11 wherein thetransmitted data window contains the determined number of proactive FECpackets and the determined number of data packets.
 13. The method ofclaim 1 wherein the step of determining a packet size comprises adaptingthe packet size from a first size to a second size smaller than thefirst size.
 14. The method of claim 13 wherein the step of determining apacket size includes increasing window granularity of the data window.15. The method of claim 1 further comprising: receiving a duplicateacknowledgement; transmitting a reactive FEC packet responsive to theduplicate acknowledgement.
 16. The method of claim 15 further comprisingdetermining a number of reactive FEC packets to transmit based on thenumber of packets expected to be received.
 17. The method of claim 15further comprising determining a number of reactive FEC packets totransmit based on the number of proactive FEC packets expected to bereceived and the estimated packet erasure rate.
 18. The method of claim1 further comprising adjusting window granularity of the data window.19. The method of claim 18 wherein the step of adjusting windowgranularity comprises adjusting the size of the packets in the datawindow.
 20. The method of claim 18 wherein adjusting window granularityis based on the number of proactive FEC packets in the data window. 21.The method of claim 1 further comprising a step of receiving an ExplicitCongestion Notification (ECN).